Although causality cannot be established in the studies assessing the relationship between vitamin B12 levels and aging, our study shows in a 12-year-old boy with an inborn error of cbl metabolism with low vitamin B12/high homocysteine levels, brain atrophy, brain circuits ́ alterations, and neuropsychological disturbances similar to those described in old populations (and thus with multiple comorbidities working as possible confounders), re-enforcing the suggested role of vitamin B12 deficiency/dysfunction on neurological aging. The gene discussed is CBL; the disease is vitamin B12 deficiency.